The present invention relates generally to the marking of ophthalmic lenses of organic material.
It is customary to apply after manufacture one or more marks or indicia on such ophthalmic lenses, such as, cross hairs or X's indicating the optical center, particularly when the optical center does not coincide with the geometric center, and/or an indication of corrective power of the lens.
Such marks are intended to facilitate the practitioner's job of mounting the lens in eyeglass frames, especially for positioning them relative to their optical center, or their contouring which is necessary to adapt them to the grooves of the frames for which they are intended.
At the present time, with regard to ophthalmic lenses of organic material, such marks or indicia are usually applied by means of a colored varnish which may later be removed with a solvent, for example, acetone or trichlorethylene.
The major drawback of such a marking procedure is that after removing the marks, which is obviously necessary before the lenses may be used because the marks locally obstruct the same, there is no indicia by which its characteristics may be easily and quickly ascertained.
However, it may be necessary, at some later date, after the ophthalmic lens has been mounted in an eyeglass frame to check its characteristics.
Furthermore, it is desirable for the ophthalmic lenses to bear a permanent indication of its origin or manufacture.
For these reasons it is already been contemplated to permanently, indelibly apply such marks.
This gives rise to the problem that such marks should remain invisible under normal conditions of use, namely normal lighting, and should not substantially impair the optical qualities of the lens on which they are applied.
According to a first known method, these marks are etched into the organic material. This is in practice a time-consuming and relatively expensive method.
According to other known methods for mineral glass lenses, the marking is accomplished by a controlled localized deposit of a metal or metallic salt on the lens, which may optionally include an ion exchange between the metal or metallic salt and the lens itself. Such a deposit is made sufficiently small so as not to be visible to the naked eye under normal lighting conditions and becomes visible by breathing on, thus fogging, the lens or under special lighting conditions, such as ultraviolet radiation.
Whether such a method is carried out in a vacuum or by electronic bombardment the deposition of such a metal or metallic salt is a delicate operation to accomplish and requires elaborate and expensive equipment. Besides, it is not readily apparent that such a marking procedure would be applicable to ophthalmic lenses of organic material.